Nitric oxide (NO) is a diatomic free radical endogenously synthesized in the human body when L-arginine is converted to L-citrulline by a class of enzymes known as nitric oxide synthases (NOS's). Since the first reports describing NO's action as an endothelium-derived relaxation factor, much research has been devoted to elucidating the pathways of NO generation and action in biological milieu. In particular, NO is involved in neurotransmission, vasodilation, immune responses (including anti-tumor and anti-microbial activities), the inhibition of platelet aggregation, and in blood pressure control. See Zhang, X., Frontiers in Bioscience, 9, 3434-3446 (2004).
Miniaturized electrochemical sensors represent promising devices for determining the spatial and temporal distributions of NO in physiology. The use of such sensors, however, has been limited by low sensitivity, comparatively slow response time, and/or interferences from other readily oxidizable biological species (e.g., nitrite, ascorbic acid, uric acid, and dopamine).
In attempts to address these limitations, a variety of permselective polymers have been synthesized and employed as sensor membranes. For example, poly(tetrafluoroethylene) (TEFLON®, E. I. du Pont de Nemours and Company, Wilmington, Del., United States of America) has proven to be a selective membrane resulting in the fabrication of nitric oxide sensors with good sensitivity. Unfortunately, the poor solubility of poly(tetrafluoroethylene) in standard organic solvents and the intricate process required to mount or coat such films onto electrodes has hindered its utility as a membrane for fabricating microsensors, including those for use in detecting and measuring nitric oxide.
Accordingly, there is a need in the art for gas permeable materials for use as sensor membranes. In particular, there is a need for gas permeable materials that can be synthesized using common solvents and via methods that can be readily modified to tailor the permeability and selectivity of the materials for a specific use and to easily coat a variety of sensor shapes and materials.